Looking at the screen, I conclude that you are using the FOS v. 5.2.
I will be happy to know how in this version check consumed bandwidth without using additional software (eg. snmp)
In FOS v. 5.4 in FortiView section now is available new column - "bandwidth" that will tell you who consumes the Internet. So you might want to think about upgrading to a newer system.
The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.